Charles f



(No Model.)

OQRSGOTT, SELF INDUCTION COIL;

Patented Jan. 23, 1894.

I50 i I 6 1 I l mo I l 1: i l

I 60 40 i E 30 a i 20 5 i 10 i fa z WIT/V588 8.

UNITED STATES PATENT OFFICE.

CHARLES F. SCOTT, OF PITTSBURG, PENNSYLVANIA, ASSIGNOR TO THE WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, OF SAME PLACE.

SELF-INDUCTION COIL.

SPECIFICATION forming part of Letters Patent No. 513,425, dated January 23, 1894.

Application filed November 25, 1892. Serial No. 453,141. (No model.)

To wZZ whom it may concern.-

--Be it known that I, CHARLES F. SCOTT, a citizen of the United States, residing in Pittsburg, in the county, of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Self-Induction Coils, (Case No. 520,) of which the following is a specification.

My invention relates to laminated cores:

used in various connections, and particularly to those used for choking coils in series incandescent lamp distribution.

One object of my invention is to provide a laminated core which shall permit the passage of a minimum current at normal voltages but shall offer as small a resistance to current as possible when the difference of potential rises beyond a given point.

Another object of my invention is the diminution of the hurtful heating effect due to rapid changes in magnetization of the iron itself.

In the accomplishment of these ends I have devised a form of choking coil shown in the accompanying drawings, wherein Figure 1 is a perspective View of a coil as made according to my invention. Fig. 2 is a diagram of circuits showing the use to which my coil is adapted. Fig. 3 is a diagram showing the curve of magnetization in two cores, one made according to previously existing practice, and the other made according to my invention. Fig. 4: is a face view of preferable forms of plate used alternately in my core.

In Fig. 2 is shown a constant potential alternating current generator at 1, which is made to feed several series of incandescent lamps, the series being in multiple arc with relation to each other. These lamps are shown at 2, and are fed from the mains 4 5. In order that on cutting out a lamp or lamps of a series, the current through the remaining lamps may not be interrupted, a by-pass through a choking coil 3 is provided at each lamp as shown. While the lamp is alight the counter electromotive force of the coil is such that almost no current passes through the same, the lamp getting all the current. For a fifty volt lamp the current thus diverted by the coil is, say, one-tenth of an ampere. hen the lamp is cutout, however, the whole current must now pass through the choking show amperes. It will be seen that at fifty volts the current passing through the coil is negligible. Supposing the lamps to require two amperes at fifty volt, the current taken by the coil at this voltage will be one-tenth of an ampere, and the generator will only have to supply two and one-tenth amperes at fifty volts to each branch. When, however, any lamp is cut out it is still necessary that the two amperes shall flow in order to keep the other lamps alight. This rise from one-tenth to two amperes through the coil causes a rapid rise of counter electromotive force and the impressed electromotive force must therefore increase as well. This increase, however, is not a proportional one, but owing to saturation of the core it follows the curve 6, so that in order to maintain the required two amperes a potential difference of about one hundred and fifty volts is required at the terminals of the coil. I11 studying the effect of so substituting the choking coil for its corresponding lamp, it is necessary to consider not only the amount of the counter electromotive force, but also the difference of phase between it and the impressed electromotive force in such a choking coil. If the counter electromotive force were exerted in direct opposition to the resultant or current-producing electromotive force, it is evident that the electromotive force available for producing current in the remaining lamps of the series would be found by simply subtracting the counter electromotive force from the constant electromotive force on the terminals of the branch, in the case above supposed, one thousand Volts. But, as is well known, the counter electromotive force in a self-induction coil is not directly opposed to the current-producing electromotive force. The phases of the two potentials are at an angle to each other, and in order to find the available electromotive force for the remaining lamps it is necessary to subtract from the constant one thousand volts, a number equal to the product of the counter electromotive force and the cosine 0f the angle of phase difference. It will be clear that this phase difference may be at such an angle that even with the counter electromotive force of one hundred and fifty volts, the loss of available voltage on the circuit is only fifty volts, or just that which was necessary in overcoming the resistance of the lamp cut out. At this critical angle the remaining lamps would be supplied with the same current as before cutting out any lamps, and their brilliancy would not be affected. The angle of phase difference may, indeed, be so great that the remaininglamps are actually made brighter when any lamp is cut out, but this effect will occur only upon cutting out the first two or three lamps, and all subsequent cutting out of lamps will render the remainder less bright. It will be evident that this dimming effect may be lessened and that a greater number of lamps may be cutout before such dimming effect occurs, if we lessen the counter electromotive force opposed by each choking coil when its lamp is out out. This can be done by lowering the point of saturation of the coil. This must be accomplished, however, without increasing the current taken by the choking coil when its proper lamp is lighted, as there would then be too great a normal shunt current and too small a ratio between the lighting current and total current supplied to each series by the mains. These ends are thus arrived at by my invention and actually reached thereby.

Fig. 1 shows the form of choking coil which has been largely used in the past. This consists of a closed magnetic circuit made up of laminated plates of the form shown in Fig. 4 at 8 built around a coil 9. The portions 10 are bent back and the coil 9 is placed in the openings 11, after which the plates are again straightened and thus the coils are inclosed. This form of choking coil broadly considered is not of my invention and needs no further description here. Since the saturation of the core is effected by an excessive increase of the density of the lines of force therein, it is evident that in order to more quickly saturate the core, some means must be devised whereby the increment of density of such lines is largely increased.

in the coils ordinarily in use the increase in lines of force necessarily takes place over the whole area of any section made across the lines of magnetic flow. The increase per unit of area or increase of density is therefore comparatively slow. If such increase could be confined to a small area and the total number of lines not be materially diminished at normal load,the increase of densitycould be made very sudden and the ends above set forth could be obtained. It is this principle which I have utilized in my invention. I take the form of plate shown at S in Fig. 4. and cut away, for instance, the portion shaded in the figure, thus producing a plate of the form shown at 12, wherein the magnetic circuit is interrupted by air-gaps at 13.

The broad principle of my invention contemplates the local reduction of cross-sectional area in the plate or pile of plates however accomplished. It is therefore evident that if desired, the same ends may be attained by the notches shown in dotted lines in Fig. 4 at 13, or the opening, instead of being made in the shaded portion of the plate shown in Fig. 8 mightoccur at 13".

Plates having been formed according to the general principle above set forth, I build up my core as shown in Fig. 1, preferably of plates alternately of the form shown in full lines at 8 and of that shown at 12. The resulting core is shown at Fig. 1, and presents numerous air-gaps as at let therein. Where the method of local reduction shown at 13 is employed, the component plates of a given core may, if desired, be all of the same shape.

Referring to Fig. 1 it will be seen that in the line of the air-gaps 14- the magnetic circuit has almost double the resistance per unit of length along lines of induction that it has in otherportions of the core. The conductance of this highly resisting portion of the circuit is nevertheless ample to avoid saturation at fifty volts. As soon, however, as the lamp is cut out and the current rises in the core the newly formed lines of force in crossing these areas of high resistance are all obliged to crowd through the portions of the plates 8, shaded in Fig. 4.. Not only must these small portions of iron carry the increased lines induced in the plates 8 to which they belong, but the lines in the alternate plates 12 finding the air-gaps 13, crowd through the reduced iron areas of plates 8. The consequence of this double duty being thrown upon these small portions of iron is that the density of lines of force in them is increased with very great rapidity and the relation of voltage and current in a coil built as in Fig. l is expressed by the current 15, wherein it will be seen that the required two amperes are allowed to pass at a voltage of only one hundred.

From the above it will be clear that the action of a core built up of plates notched as at 13 is the same in principle as that of the core shown in Fig. 1. The object to be attained is the local crowding of lines of force through a narrow path, such path being sulficient to carry the normal induction when the lamp is lighted without saturation, but owing to its smaller area producingamore rapid increase of density in proportion to the increase of total induction than is found in other parts of the core.

It will be seen that the total heating effect in the core as made according to my inven- ICC) crate normally under a certain critical load,

said core having a locally reduced cross sectlon of only just suflicient conductance to remain unsaturated under said critical load,

substantially as described.

2. An electro-magnetic core adapted to operate normally under a certain critical load,

said core being composed of magnetic plates containing two apertures containing magnetizing coils, some of said plates having cross-sections locally reduced to such an extent as to have a total amount of magnetic material at such sections just sufficient to carry the lines of force at said critical load without saturation, substantially as described.

3. A laminated core for induction coils composed of plates having complete and incomplete iron circuits alternately, substantially as described.

4;. A laminated core for induction coils composed of plates having two apertures for containing the coils, every alternate plate having one or more gaps through its periphery at one corner of one of said apertures, substantially as described.

In testimony whereof I have hereunto sub,- scribed my name this 14th day of November, A. D. 1892.

CHAS. F. SCOTT.

Witnesses:

JAMES WM. SMITH, HAROLD S. MAOKAYE. 

